Tensile and interfacial properties of radially aligned CNT grown carbon fibers

Abstract

The relatively high mass-specific strength and stiffness of carbon fibers (CFs) has established CF reinforced plastics (CFRPs) as the benchmark material for next-generation aerospace structures. While CFRPs with radially-grown aligned carbon nanotubes (CNTs), termed fuzzy fiber reinforced plastics (FFRPs), have exhibited enhanced inter- and intralaminar mechanical properties on model FRP systems, these results have not been replicated for aerospace-grade CFRP due to challenges in manufacturing. This thesis reports a scaled (weave- vs. tow-level) manufacturing method of fuzzy woven CFRPs designed to yield dense and aligned CNT coverage on the fibers, and retain the fiber tensile and interface properties. These challenges were explored through mechanical testing, in addition to numerical reactive computational fluid dynamics (CFD) CNT growth models. Single fiber tensile tests for fuzzy fibers from aerospace-grade CF weaves showed no reduction in tensile strength compared to baseline (as received) fibers. Continuously monitored single fiber composite fragmentation testing revealed a 34% decrease in fiber-matrix interfacial shear strength (IFSS) for sized (polymer coating on fibers) fuzzy fibers, attributed to thermally induced sizing transformations during CNT growth, whereas the fuzzy de-sized fibers exhibited no reduction in IFSS. The CFD model demonstrated gas depletion trends correlated to the areas of substandard growth and a high sensitivity to the surface-to-volume ratio of the porous woven substrate. Retained CF properties supports this facile, scaled manufacturing method's ability to disperse CNTs uniformly on CF weaves to create a laminate-level fuzzy CFRP towards enhanced mechanical and multifunctional properties. With continued CNT growth modeling efforts, further scaling of this fuzzy CFRP architecture could be integrated into commercial manufacturing processes.